configure/Makefile: Include contrib in "make dist"

Change-Id: I2d6a2e06f075391e8e51d1342a1afe955cc127b0
diff --git a/contrib/Makefile.am b/contrib/Makefile.am
new file mode 100644
index 0000000..17f56ed
--- /dev/null
+++ b/contrib/Makefile.am
@@ -0,0 +1,3 @@
+SUBDIRS = etc_default systemd
+
+EXTRA_DIST = remsim-apitool.py owhw-event-script.sh